1. Field of the Invention
This invention relates to a sound field reproduction apparatus and a sound field space reproduction system that provide a virtual reality space with an effect of reality sensation.
This application claims priority of Japanese Patent Application No. 2003403592, filed on Dec. 2, 2003, the entirety of which is incorporated by reference herein.
2. Related Background Art
Speakers are or a stereo headphone is used to reproduce a three-dimensional sound field. When speakers are used, the sound field is reproduced in a listening area that spreads to a certain extent. Since the sound field is synthetically reproduced, the listener in the sound field can perceive exactly what is supposed to be perceived in the sound field. When, on the other hand, a stereo headphone is used, the sound that is supposed to be reproduced to the ears of a listener who is in the sound field is reproduced to the ears of the listener by controlling the waveform that is reproduced and conveyed to the ears of the listener.
With conventional reproduction of three-dimensional sound field, the listener places him- or herself at a predetermined virtual listening position, which is a fixed position, in a space of virtual reality so as to listen to reproduced sounds coming from a fixed or moving virtual sound source. With this technique, however, the listener can listen only to the sounds that get to the specified listening position and its vicinity in a virtual reality space. In other words, it is not possible to reproduce a sound field space in such a way that the listener can freely move in a virtual space.
To cope with this problem, patent Document 1 (Japanese Patent Application Laid-Open Publication No. 7-312800) proposes a technique of producing a sound image that matches the position, the direction, the moving speed and the moving direction of the listener and those of each of the sound sources in a sound field space that is produced by processing direct sounds, initial reflected sounds and reverberated sounds, taking the characteristics of the sound field space into consideration, on an assumption that the listener uses a stereo headphone.
However, the technique described in patent Document 1 (Jpn. Pat. Appln. Laid-Open Publication No. 7-312800) only makes it possible to reproduce a space to the sense of hearing. In other words, the listener cannot perceive a sensation of freely moving in a virtual reality space or that of free fall.
Additionally, when a sound field is reproduced by way of a stereo headphone, the listener cannot share the produced sound field space with other listeners. In other words, the listener cannot enjoy conversations with other listeners on the reproduced sound field. For example, it is not possible to provide such a space to the passengers in a moving vehicle or in a dining car.
As for reproducing a space, a listener can acquire an acoustic perception of moving in a space when actual sound sources are arranged in a listening room and the listener moves in the room. However, it is then necessary to prepare a full-size sound field space and such an arrangement is unrealistic.